This invention relates to a method and apparatus for positioning semiconductor flip chips onto transfer probes for aligning the chips with conductive lead frame structures for bonding. More particularly, it involves a cartridge-type positioning apparatus and a method of using it to successively position semiconductor flip chips onto a magnetized probe which raises the chips from the positioning apparatus and automatically aligns the chips with corresponding fingers of a conductive lead frame so that it can be bonded thereto.
This invention is a production improvement on U.S. Pat. application Ser. No. 414,274, "Magnetic Alignment for Semiconductor Device Bonding", Hartleroad et al, filed concurrently with this application and assigned to the same assignee. In U.S. Pat. application Ser. No. 414,274, now U.S. Pat. No. 3,887,997, there is disclosed a method and apparatus for aligning integrally leaded semiconductors by chips with conductive lead frame structures. In that application, a chip is manually placed on one end of a transfer probe and raised to within close proximity of an overlying set of lead frame fingers. A magnetic force transmitted through the probe automatically orients the integral chip leads with their corresponding lead frame fingers and simultaneously raises the chip off of the probe into engagement with the fingers so that the chips can be bonded thereto. The manual placement of the chip on the transfer probe has proved to be inefficient in high volume production. Furthermore, it has been discovered that the most consistent precise alignment occurs when the integral chip leads are generally aligned with their corresponding lead frame fingers before the chip is magnetically transferred thereto.
A flip chip is an integrally leaded semiconductor device die in which the integral leads extend perpendicularly from a major chip face. These integral leads are often referred to as contact bumps which are extensions of a conductor pattern on the chip face, and serve as electrical interconnection points for larger conductive leads.
It is commonplace in semiconductor device manufacturing to process hundreds of these flip chips simultaneously as part of a single wafer. One of the methods to separate the discrete devices from the wafer is to saw a grid pattern in the wafer between adjacent rows and columns of discrete devices. In the pattern, each discrete device is thus separated from adjacent devices by a surrounding grid pattern. The grid pattern extends more than halfway through the thickness of the wafer. As is known in the art, the wafer is affixed to a flexible, adhesive strip. The back side of the strip is then pulled over a sharp edge to break up the wafer to form a plurality of semiconductor chips, each of which contains a discrete semiconductor device. This dicing method, as it is commonly referred to, leaves burrs on each chip which extends laterally from the lower side portions of the chip that have not been sawed away.
We have invented an apparatus and method of using it which utilizes these burrs to successively position semiconductor flip chips onto the transfer probe disclosed in U.S. Pat. application Ser. No. 414,274, "Magnetic Alignment for Semiconductor Device Bonding", Hartleroad et al.